Nanomaterials to boost solar cell efficiencies

Two new solar cell designs are using light-directing nanomaterials to develop thin-film solar cells with record-breaking conversion efficiencies.

Developed by electrical engineers at the University of California, San Diego, the technologies aim to break the theoretical limit of 31 percent sunlight-to-energy conversion efficiency for conventional single-junction solar cells.

The research has received US$885,000 in funding from the U.S. Department of Energy’s Solar America program.

One team of engineers is using nanoparticles to scatter incoming light particles, called photons, into paths within the quantum well region in which energy is absorbed.

The new design approaches the problem of increasing the probability of photon absorption in a different manner to previous efforts of stacking several quantum-well layers.

“Our devices have a much thinner stack of quantum wells, which means the extra photons that are absorbed are much more likely to make it out of the quantum wells and generate current,” explained principal investigator Edward Yu.

“This enables high photon absorption efficiency, high electron and hole collection efficiency – and therefore also high voltage – to be achieved simultaneously.”

Using the light-scattering design, engineers have achieved a sunlight-to-energy conversion efficiency of 45 percent. The approach is expected to reach higher efficiencies as more aspects of the technology are optimised.

A second team of engineers have included nanowires in the solar cell design, which serve as electron superhighways that attract solar energy an electrode, to be converted to electricity.

“If you provide electrons with a defined pathway to the electrode, you can reduce some of the inefficiencies that currently plague thin-film solar cells made from polymer mixtures,” explained Clint Novotny, a recent electrical engineering Ph.D. at the University who authored a recently published research paper about the research.

Using the nanowire-spiked solar cell design, researchers have increased electrical current by six to seven orders of magnitude when compared with a polymer-only cell.